HTML radio buttons allowing multiple selections

Question

In my HTML form, I have the following as a set of radio buttons; depending on which radio button you select, the next form fieldset> is revealed; all of this works. The issue is that, for some reason, they behave like a check box rather than a radio button. As a result, you can select all options rather than just one at a time.

Can anyone see where the code below is going wrong?

<fieldset>
        <legend>Please select one of the following</legend>
        <input type="radio" name="track" id="track" value="track" /><label for="track">Track Submission</label><br />
        <input type="radio" name="event" id="event" value="event"  /><label for="event">Events and Artist booking</label><br />
        <input type="radio" name="message" id="message" value="message" /><label for="message">Message us</label><br />
  </fieldset>